1. Field of the Invention
The present application is generally drawn to nuclear steam generator examination and repair equipment.
2. Description of the Prior Art
Much of the maintenance performed in nuclear power plants is similar to that of conventional non-nuclear systems. However, nuclear systems are unique in that many components are inaccessible, due to the radiation levels.
In the early years of nuclear power, much of the maintenance was performed manually by workers entering the steam generator head. As maintenance activities and radiation levels increased, it became increasingly difficult to perform steam generator repairs manually. Because inspecting the large number of steam generator tubes is mandatory during refueling outages, this work was a logical candidate for applications of early remote technology. The first manipulator used on Once through Steam Generators (OTSG's) was positioned manually on the tubesheet, locked in place, then computer controlled from a remote location. The manipulator was then moved manually to the next location. For Recirculating Steam Generators (RSG's), an articulated arm manipulator was used having an arm for holding video and or cleaning equipment which was vertically movable into the tube bundle. Although also manually installed, it was not computer controlled. Both manipulators performed well for inspection, but they could not support the heavy tools required for plugging and other tube repair operations. For this reason and also for reduced radiation dose limits, the practice of manually installing the manipulators had to be eliminated.
Development of an advanced manipulator was based on the following criteria:
1. must be installed with no human entry in the steam generator,
2. must perform inspection and repair duties,
3. must access all tubes, and
4. must be computer controlled.                One of the remote manipulator designs is shown in FIG. 1. Named ROGER® (Remotely Operated Generator Examination and Repair); it is covered by U.S. Pat. No. 4,804,038 and was placed in service in the mid nineteen eighties. The unit is installed in the steam generator head by a series of cables and pulleys as shown in FIG. 2. Although light weight in construction, it has a load capacity of 200 lb (91 kg). Once calibrated, the toolhead can be remotely moved to any tube location within the region it was installed with the exception of the mounting location, or “exclusion zone”. With the exception of tool head installations, all operations are remotely controlled and monitored by video equipment. The control station is located outside of the containment building and control signals are often multiplexed to reduce the number of cables that must be routed to the building.        One problem was that the manipulator had to be manually moved to different regions within the steam generator. This allows access to the tubes that were in the exclusion zones. Personnel expended time and dose exposure to relocate the manipulator to the desired region. This was especially a problem when personnel were not very experienced.        